/* CirKit: A circuit toolkit
 * Copyright (C) 2009-2015  University of Bremen
 * Copyright (C) 2015-2017  EPFL
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 */

/**
 * @file thread_pool.hpp
 *
 * @brief Thread pool
 *
 * based on an implementation of Jakob Progsch and Václav Zeman
 * (see copyright notice below)
 * https://github.com/progschj/ThreadPool
 *
 * @author Mathias Soeken
 * @since  2.3
 */

#ifndef THREAD_POOL_HPP
#define THREAD_POOL_HPP

#include <condition_variable>
#include <functional>
#include <future>
#include <memory>
#include <mutex>
#include <queue>
#include <thread>
#include <vector>

namespace cirkit
{

class thread_pool
{
public:
  /* number of threads is the same as number of cores */
  thread_pool();
  thread_pool( unsigned num_threads );
  ~thread_pool();

  template<class F, class... Args>
  auto enqueue( F&& f, Args&&... args ) -> std::future<typename std::result_of<F(Args...)>::type>
  {
    using return_type = typename std::result_of<F(Args...)>::type;

    auto task = std::make_shared<std::packaged_task<return_type()>>(
        std::bind( std::forward<F>( f ), std::forward<Args>( args )... )
      );

    std::future<return_type> res = task->get_future();
    {
      std::unique_lock<std::mutex> lock( queue_mutex );

      /* don't allow enqueueing after stopping the pool */
      if ( stop )
      {
        throw std::runtime_error( "enqueue on stopped thread pool" );
      }

      tasks.emplace( [task]() { (*task)(); } );
    }

    condition.notify_one();
    return res;
  }

private:
  std::vector<std::thread>          workers;
  std::queue<std::function<void()>> tasks;
  std::mutex                        queue_mutex;
  std::condition_variable           condition;
  bool                              stop = false;
};

}

#endif

/* from: https://github.com/progschj/ThreadPool/blob/master/COPYING

Copyright (c) 2012 Jakob Progsch, Václav Zeman

This software is provided 'as-is', without any express or implied
warranty. In no event will the authors be held liable for any damages
arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:

   1. The origin of this software must not be misrepresented; you must not
   claim that you wrote the original software. If you use this software
   in a product, an acknowledgment in the product documentation would be
   appreciated but is not required.

   2. Altered source versions must be plainly marked as such, and must not be
   misrepresented as being the original software.

   3. This notice may not be removed or altered from any source
   distribution.

*/

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